Methods of determining the optimal erase and write power, and recording apparatus with devices for said methods

ABSTRACT

The application relates to methods and devices for determining the optimal erase ( 17 ) and write powers for erasing and writing information on an optical record carrier ( 85 ). These optimal powers are determined from two powers, P min  ( 15 ) and P max  ( 16 ), found at specific points, ( 22 ) and ( 24 ), in a curve ( 10 ) where the normalized reflected power ( 12 ) is plotted versus the test power ( 11 ).

[0001] The invention relates to a method of determining the optimalerase power for erasing marks provided in an optical record carrier ofthe type in which marks are provided by locally heating the recordcarrier with radiation pulses having a sufficiently high power so as tocause changes in optical properties of the record carrier, which changesbecome manifest by a reduced reflection of the radiation pulses.

[0002] The invention also relates to a method of determining the optimalwrite power for providing marks in an optical record carrier, whichmarks are provided by locally heating the record carrier with radiationpulses having a sufficiently high power so as to cause changes inoptical properties of the record carrier, which changes become manifestby a reduced reflection of the radiation pulses.

[0003] The invention further relates to an optical record carrier foruse in one of the methods according to the invention, inscribable by aradiation beam, containing an area comprising information aboutproperties of the optical record carrier.

[0004] The invention further relates to a recording apparatus comprisinga calibration device for determining the optimal erase power requiredfor erasing marks provided in an optical record carrier of the type inwhich marks are provided by locally heating the record carrier withradiation pulses having a sufficiently high power so as to cause changesin optical properties of the record carrier, which changes becomemanifest by a reduced reflection of the radiation pulses.

[0005] The invention further relates to a recording apparatus comprisinga calibration device for determining the optimal write power requiredfor providing marks in an optical record carrier, which marks areprovided by locally heating the record carrier with radiation pulseshaving a sufficiently high power so as to cause changes in opticalproperties of the record carrier, which changes become manifest by areduced reflection of the radiation pulses.

[0006] The invention also relates to a calibration device for use in arecording apparatus.

[0007] The optimal erase power and the optimal write power are dependenton properties of the record carrier used and on the properties of therecording apparatus. These powers should therefore be determinedwhenever a given record carrier is used in a recording apparatus.

[0008] Methods and apparatuses for determining these powers are known,inter alia, from EP 0 737 962 (Ricoh Company Ltd). This applicationdescribes a method in which the optimal write power is determined withreference to a modulation power curve to be fixed for each combinationof record carrier and recording apparatus. The modulation power curve isfixed by providing marks in the record carrier through a large range ofwrite powers (P_(W)) and by subsequently measuring the modulation (m) ofthe associated marks for each write power, i.e. the reflected powercoming from a mark relative to the reflected power coming from an areawithout marks. The modulation values thus obtained are plotted versusthe associated write powers in the modulation power curve (m(P_(W))).Subsequently, a curve (the γ curve) is determined which represents thenormalized first-order derivative (γ=(dm/dP_(W)).(P_(W)/m)) of themodulation power curve (m(P_(W))) described hereinbefore. This γ curvehas an asymptotic variation, with only a slight decrease of the γoccurring at higher write powers. The optimal write power is found byselecting the power which is associated with a predetermined value ofthe derivative γ. The optimal erase power is subsequently linearlydependent on the optimal write power found.

[0009] The determination of an unambiguous value from an asymptoticallyvarying curve, such as the γ curve, is not very well possible. Smallvariations of the input value, the predetermined value of γ, may resultin large variations of the output value, the optimal write power.Moreover, when determining the modulation power curve, write powers areused which lie above the optimal write power so that unnecessarily hightemperatures are caused in the record carrier.

[0010] It is an object of the invention to provide a method ofunambiguously determining the optimal erase power and to provide amethod of unambiguously determining the optimal write power, avoidingunnecessarily high temperatures in the record carrier.

[0011] According to the invention, this object is achieved by means of amethod of determining the optimal erase power, which is characterized inthat the method comprises a preparatory step of providing marks on therecord carrier by locally heating the record carrier with radiationpulses having a first power, followed by a first measuring step ofdetermining a second power (P_(min)) of the radiation pulses, at whichpower the optical properties of the record carrier at the location ofthe marks provided in the preparatory step do not substantially changewhen the record carrier is irradiated at a power which is lower thansaid second power, and the optical properties of the record carrier atthe location of the provided marks change when the record carrier isirradiated at a power which is higher than said second power, such thatthe normalized reflected power increases, and a second measuring step ofdetermining a third power (P_(max)) of the radiation pulses, at whichpower the optical properties of the record carrier change to such anextent that the normalized reflected power becomes maximal, when therecord carrier is irradiated at said third power at the location of themarks provided in the preparatory step, followed by a comparison step ofdetermining the optimal erase power (P_(EO)) from the equation$P_{EO} = {\beta \cdot \frac{\left( {P_{\min} + P_{\max}} \right)}{\alpha}}$

[0012] in which α is a constant known in advance and β is a variablewhich is dependent on properties of the record carrier. The normalizedreflected power (R) is understood to mean the reflected power relativeto the power at which the record carrier is irradiated.

[0013] An advantage of this method is that the powers P_(min) andP_(max) to be determined, from which the optimal erase power follows viaan equation, can be unambiguously determined because they are located atpoints of inflection in a curve in which the normalized reflected power(R) is plotted versus the power (P) at which the record carrier isirradiated at the location of the marks provided in the preparatorystep. This means that the first-order derivative dR/dP exhibits anabrupt variation in value or sign at the powers P_(min) and P_(max) sothat these powers can be determined in a simple and unambiguous manner.A further advantage of the method appears to be that the determinedpowers, P_(min) and P_(max), are hardly dependent on the write methodwith which the marks are provided on the record carrier in thepreparatory step. Also the number of times of consecutively performingthe method, in which marks are each time provided at the same positionon the record carrier, has no significant influence on the determinedpowers P_(min) and P_(max).

[0014] According to the invention, this object is further achieved bymeans of a method of determining the optimal write power, which ischaracterized in that the method comprises a preparatory step ofproviding marks on the record carrier by locally heating the recordcarrier with radiation pulses having a first power, followed by a firstmeasuring step of determining a second power (P_(min)) of the radiationpulses, at which power the optical properties of the record carrier atthe location of the marks provided in the preparatory step do notsubstantially change when the record carrier is irradiated at a powerwhich is lower than said second power, and the optical properties of therecord carrier at the location of the provided marks change to such anextent that the normalized reflected, power increases, when the recordcarrier is irradiated at a power which is higher than said second power,and a second measuring step of determining a third power (P_(max)) ofthe radiation pulses, at which power the optical properties of therecord carrier change when the record carrier is irradiated at saidthird power at the location of the marks provided in the preparatorystep, such that the normalized reflected power becomes maximal, followedby a comparison step of determining the optimal write power (P_(WO))from by the equation$P_{WO} = {\delta \cdot \beta \cdot \frac{\left( {P_{\min} + P_{\max}} \right)}{\alpha}}$

[0015] in which α is a constant known in advance and β and δ arevariables which are dependent on properties of the record carrier.

[0016] Also in this method, the powers, P_(min) and P_(max), can beunambiguously determined because they are located at points ofinflection in a curve in which the normalized reflected power (R) isplotted versus the power (P) at which the record carrier is irradiatedat the location of the marks provided in the preparatory step, and thedetermined powers, P_(min) and P_(max), are hardly dependent on thewrite method and on the number of times of performing the method.

[0017] The methods described are applicable, inter alia, when usingoptical record carriers of the “phase change” type, in which marks areprovided in the record carrier by locally heating the record carrier,under the influence of which a local transition takes place from acrystalline state to an amorphous state, and vice versa.

[0018] An embodiment of the method according to the invention ischaracterized in that the first measuring step comprises at least twosub-steps, in which sub-steps the record carrier is irradiated at thelocation of the provided marks with radiation pulses having a test powerof a selected value, which test power increases in the consecutivesub-steps as long as the optical properties of the record carrier at thelocation of the irradiated marks do not substantially change, and whichsub-steps are terminated as soon as the optical properties of the recordcarrier at the location of the irradiated marks change to such an extentthat the normalized reflected power increases, followed by a first finalstep in which the value of the test power in the last sub-step isallocated to the second power (P_(min)).

[0019] An advantage of this embodiment is that the sequence ofconsecutive sub-steps is terminated by a clear stop criterion becausethe normalized reflected power upon irradiation at a test power justabove the second power (P_(min)) exhibits a fairly abrupt increase withrespect to the normalized reflected power upon irradiation at a testpower just below the second power (P_(min)).

[0020] An embodiment of the method according to the invention ischaracterized in that the second measuring step comprises at least twosub-steps, in which sub-steps the record carrier is irradiated at thelocation of the provided marks with radiation pulses having a test powerof a selected value, which test power increases in the consecutivesub-steps and which sub-steps are terminated as soon as the opticalproperties of the record carrier at the location of the irradiated markschange to such an extent that the normalized reflected power decreases,followed by a second final step in which the value of the test power inthe last sub-step is allocated to the third power (P_(max)).

[0021] An advantage of this embodiment is that the sequence ofconsecutive sub-steps is terminated by a clear stop criterion becausethe normalized reflected power upon irradiation at a test power justabove the third power (P_(max)) exhibits a fairly abrupt decrease withrespect to the normalized reflected power upon irradiation at a testpower just below the third power (P_(max)). A further advantage of thisembodiment is that the test powers do not become higher than the minimalpower which is required for providing marks. Consequently, the recordcarrier is not irradiated with radiation pulses having an unnecessarilyhigh test power, so that no unnecessarily high temperatures are causedin the record carrier.

[0022] An embodiment of the method according to the invention ischaracterized in that the marks, which are provided in the preparatorystep, are of a maximum length which maximum length is the maximum lengthallowed by the applied coding method.

[0023] In this embodiment, the longest possible marks are provided whichare allowed within the scope method. For example, a mark with a lengthof (d+1) times the channel-bit-length (.e., a I(d+I) carrier) isprovided when a (d,k) RLL coding method is applied.

[0024] The length of these longest possible marks is at least largerthan the diameter of the cross-section of the beam of radiation pulseswith respect to the record carrier. An advantage of this embodiment isthat, due to the provision of these marks, a maximally unambiguoustransition in normalized reflected power (R) is obtained between a markand an area without marks. This is particularly important where theoptical properties of a record carrier at the location of a mark differonly slightly from the optical properties in an area without marks.

[0025] An embodiment of the method according to the invention ischaracterized in that the marks, which are provided in the preparatorystep, are coded with an I11 carrier in accordance with the EFM+(Eight-to-Fourteen Modulation Plus) coding method.

[0026] In this embodiment, the longest possible marks are provided whichare possible within the scope of the EFM+ coding method, which method isused, inter alia, in DVD systems.

[0027] An embodiment of the method according to the invention ischaracterized in that the marks, which are provided in the preparatorystep, are provided in selected distinguishable areas.

[0028] For example, the marks may be provided in a limited number ofsectors of a track. An advantage of this embodiment is that themeasuring steps can be performed more rapidly than when the marks areprovided in larger areas such as, for example, a complete track.

[0029] An embodiment of the method according to the invention ischaracterized in that the selected distinguishable areas are evenlyspread across the surface of the record carrier.

[0030] An advantage of this embodiment is that irregularities in theoptical properties of the record carrier, which are not evenly spreadacross the surface of the record carrier, have a smaller influence onthe results of the measuring steps than in the case where thedistinguishable areas are not evenly spread across the surface of therecord carrier. By using areas which are evenly spread across thesurface of the record carrier, optimal values for the erase power andthe write power applying to the entire record carrier are found.

[0031] An embodiment of the method according to the invention ischaracterized in that the factor α in the comparison step has a value of2.

[0032] Although it is evident to those skilled in the art that thefactor α may assume any value between (P_(min)+P_(max))/P_(min) and(P_(min)+P_(max))/P_(max), it was found in measurements that at a valueof 2 for the factor of α, the method yields a good approximation of theoptimal erase power and write power if β is assumed to be ≈1.

[0033] An embodiment of the method according to the invention ischaracterized in that the factor α in the comparison step has a value of2 and the factor β in the comparison step has a value of between 0.7 and1.3.

[0034] Measurements proved that a value of β in said range appeared toyield an optimal value for the erase power and the write power, with thevalue for β at which these optimal values are reached being dependent onthe properties of the record carrier used.

[0035] An embodiment of the method according to the invention ischaracterized in that the factor β in the comparison stage is read froman area on the record carrier, which area comprises information aboutproperties of the record carrier.

[0036] Since the value for β, at which the optimal values for the erasepower and the write power are reached, is dependent on the properties ofthe record carrier used, this value can be determined once during theproduction of the record carrier and fixed on this record carrier.

[0037] It is a further object of the invention to provide an opticalrecord carrier for use in one of the methods according to the invention.

[0038] An optical record carrier according to the invention ischaracterized in that the area comprising information about propertiesof the record carrier comprises a value for the factor β used in thecomparison stage of the method according to the invention.

[0039] An optical record carrier according to the invention ischaracterized in that the area comprising information about propertiesof the record carrier comprises a value for the factor δ used in thecomparison stage of the method according to the invention.

[0040] Since the value for β, respectively δ, at which the optimalvalues for the erase power and the write power are reached is dependenton the properties of the record carrier, this value can be determinedonce during the production of the record carrier and can subsequently bestored in an area on the record carrier comprising information aboutproperties of the record carrier.

[0041] Such an area is for example the so-called pregroove in thelead-in area on a Compact Disk Recordable (CD-R). This pregroove isfrequency-modulated with an auxiliary signal and information aboutproperties of the record carrier are coded in the auxiliary signal. Adescription of a record carrier having such information recorded in thepregroove may be found in EP 0 397 238. Another example of such an areais a control area on a record carrier, which record carrier is dividedin an information recording area for writing user information, and acontrol area for storing information relevant for writing, reading anderasing information on the record carrier. A encoded value for β,respectively δ, may be stored as a pattern of marks in this controlarea. The control area may be embossed.

[0042] Recording media of a different type, such as for example anoptical type, may be provided with information about properties of therecord carrier in a different manner, for example, by arranging an areacomprising information about properties of the optical record carrier atthe beginning of the tape or along an auxiliary track.

[0043] Other information about properties of the record carriers whichcould be stored in the area on the record carrier comprising informationabout properties of the record carrier include for example one or morespeeds of recording, fixed power levels of the radiation beam usedduring the recording, such as a bias power level, and the duration andduty cycles of radiation pulses.

[0044] An embodiment of the method according to the invention ischaracterized in that the factor δ in the comparison step is read froman area on the record carrier, which area comprises information aboutproperties of the record carrier.

[0045] Since the value for δ, at which the optimal value for the writepower is reached, is dependent on the properties of the record carrierused, this value can be determined once during the production of therecord carrier and fixed on this record carrier.

[0046] It is a further object of the invention to provide a recordingapparatus using the method of determining the optimal erase power, and arecording apparatus using the method of determining the optimal writepower.

[0047] A recording apparatus according to the invention is characterizedin that the calibration device is adapted to provide marks on the recordcarrier by locally heating the record carrier with radiation pulseshaving a first power, and to determine a second power (P_(min)) of theradiation pulses, at which power the optical properties of the recordcarrier at the location of the provided marks do not substantiallychange when the record carrier is irradiated at a power which is lowerthan said second power, and the optical properties of the record carrierat the location of the provided marks change when the record carrier isirradiated at a power which is higher than said second power, such thatthe normalized reflected power increases, and to determine a third power(P_(max)) of the radiation pulses, at which power the optical propertiesof the record carrier change to such an extent that the normalizedreflected power becomes maximal, when the record carrier is irradiatedat said third power at the location of the provided marks, and todetermine the optimal erase power (P_(EO)) from the equation$P_{EO} = {\beta \cdot \frac{\left( {P_{\min} + P_{\max}} \right)}{\alpha}}$

[0048] in which α is a constant known in advance and β is a variablewhich is dependent on properties of the record carrier.

[0049] A recording apparatus according to the invention is characterizedin that the calibration device is adapted to provide marks on the recordcarrier by locally heating the record carrier with radiation pulseshaving a first power, and to determine a second power (P_(min)) of theradiation pulses, at which power the optical properties of the recordcarrier at the location of the provided marks do not substantiallychange when the record carrier is irradiated at a power which is lowerthan said second power, and the optical properties of the record carrierat the location of the provided marks change to such an extent that thenormalized reflected power increases, when the record carrier isirradiated at a power which is higher than said second power, and todetermine a third power (P_(max)) of the radiation pulses, at whichpower the optical properties of the record carrier change when therecord carrier is irradiated at said third power at the location of theprovided marks, such that the normalized reflected power becomesmaximal, and to determine the optimal write power (P_(WO)) from theequation$P_{WO} = {\delta \cdot \beta \cdot \frac{\left( {P_{\min} + P_{\max}} \right)}{\alpha}}$

[0050] in which α is a constant known in advance and β and δ arevariables which are dependent on properties of the record carrier.

[0051] These and other aspects of the invention are apparent from andwill be elucidated with reference to the embodiments describedhereinafter.

[0052] In the drawings:

[0053]FIG. 1 is a graph showing diagrammatically the relation betweenthe normalized reflected power (R) and the test power (P) at which therecord carrier is irradiated at the location of the marks provided inthe preparatory step,

[0054]FIG. 2 is a graph showing examples of the results of a number ofmeasurements of the normalized reflected power (R) as a function of thetest power (P),

[0055]FIG. 3 shows a flow chart of a method according to the invention,

[0056]FIG. 4 shows flow charts of embodiments of a method according tothe invention, and

[0057]FIG. 5 is a block diagram of a calibration device in a recordingapparatus according to the invention.

[0058] The curve (10) in FIG. 1 shows diagrammatically the relationbetween the test power, P, at which the record carrier is irradiated(11) at the location of the marks provided in the preparatory step, andthe normalized reflected power, R, (12). The second power, P_(min), (15)is the power at which the curve has a point of inflection (22) locatedbetween an area having a substantially constant normalized reflectedpower (21) and an area having an increasing normalized reflected power(23). The third power, P_(max), (16) is the power at which thenormalized reflected power is maximal, R_(max), (19). This is also thepower at which the curve has a point of inflection (24) located betweenan area having an increasing normalized reflected power (23) and an areahaving a decreasing normalized reflected power (25). The optimal erasepower (17) is between P_(min) (15) and P_(max) (16).

[0059]FIG. 2 is a graph showing examples of the results of a number ofmeasurements (31 through 34) of the normalized reflected power, R, (12)as a function of the test power, P, (11) in arbitrary units. Inmeasurement 31, a write method for providing marks in the preparatorystep is used, which deviates from the write method used in measurements32 through 34. The measurements 31 and 32 were performed on a recordcarrier on which no previous measurements had been performed. Themeasurements 33 and 34 were performed on a record carrier on which 100previous measurements had been performed in measurement 33 and 1000 inmeasurement 34, at which the marks were always provided in the sameposition on the record carrier. The measurements shown in the graphprove that P_(min) (15) and P_(max) (16) are relatively independent ofthe write method used and of the number of times of performing themeasurements on one and the same record carrier.

[0060]FIG. 3 shows a flow chart of a method according to the invention.In the preparatory step (40), marks are provided on the record carrier.Subsequently, the second power, P_(min), can be determined in a firstmeasuring step (41), followed by determining the third power, P_(max),in a second measuring step (42). After the preparatory step (40), thethird power, P_(max), can be determined in a second measuring step (42),followed by determining the second power, P_(min), in the firstmeasuring step (41). When both measuring steps have been performed, theoptimal value for the erase power and the write power, respectively, isdetermined in the comparison step (43).

[0061]FIG. 4A shows a flow chart of an embodiment of the first measuringstep (41) for determining P_(min), and FIG. 4B shows a flow chart of anembodiment of the second measuring step (42) for determining P_(max). Inblock 51, an initial value of 1 is allocated to a counter, n, whichkeeps track of the number of sub-steps performed. Subsequently, in block52, the record carrier is irradiated at the location of the marksprovided in the preparatory step (40) with radiation pulses having atest power of a selected value, P(1), and the normalized reflectedpower, R(1), associated with this test power is measured. In block 53,the counter, n, which keeps track of the number of sub-steps performedis raised by 1. In block 54, the record carrier is subsequentlyirradiated at the location of the marks provided in the preparatory step(40) with radiation pulses having a test power of a value P(n), in whichP(n) is larger than the value of the test power in the previous stepP(n−1), and the normalized reflected power, R(n), associated with thistest power is measured.

[0062] In comparison block 551 in FIG. 4A, the normalized reflectedpower in the current sub-step, R(n), is compared with the normalizedreflected power in the previous sub-step, R(n−1). If the two powers aresubstantially equal, the blocks 53 and 54 are repeated via path 581. Ifthe two powers are not substantially equal, the value of the test powerin the last sub-step, P(n), is allocated to P_(min) in block 561 viapath 591.

[0063] In comparison block 552 in FIG. 4B, the normalized reflectedpower in the current sub-step, R(n), is compared with the normalizedreflected power in the previous sub-step, R(n−1). If the value of R(n)is smaller than the value of R(n−1), the value of the test power in thelast sub-step, P(n), is allocated to P_(max) in block 562 via path 592.If the value of R(n) is not smaller than the value of R(n−1), the blocks53 and 54 are repeated via path 582.

[0064]FIG. 5 is a block diagram of a calibration device (60) in arecording apparatus according to the invention. Block 81 shows anoptical system in the recording apparatus, which optical systemirradiates an optical record carrier (85) with radiation pulses (84) andreceives reflected radiation pulses and converts them into aninformation signal (71). The optical system (81) is driven by a block(82) with control logics. This control logics block (82) controls, interalia, the power of the radiation pulses (84). The calibration device(60) comprises a block (61) with control logics for performing thepreparatory step in accordance with the inventive methods, a block (62)with control logics for performing a first measuring step in accordancewith the invented methods, a block (63) with control logics forperforming the second measuring step in accordance with the inventedmethods, and a block (64) with control logics for performing thecomparison step in accordance with the invented methods.

[0065] Block 61 sends information to the control logics (82) via acontrol signal 72, which information is necessary for providing marks onthe optical record carrier (85). Blocks 62 and 63 send information tothe control logics (82) via control signal 73, which information isnecessary for performing the measuring steps. Information signal (71)supplies the blocks 62 and 63 with information about the reflectedradiation pulses. Block 62 supplies the result of the first measuringstep via signal 75, and block 63 supplies the result of the secondmeasuring step to block 64 via signal 76. This block 64 supplies theoptimal erase power and the optimal write power, respectively, viasignal 79 to the recording apparatus. Information about the parameters βand δ is obtained via information signal 71 from the optical recordcarrier (85), or via signal 78 from the recording apparatus.

1. A method of determining the optical erase power for erasing marksprovided in an optical record carrier of the type in which marks areprovided by locally heating the record carrier with radiation pulseshaving a sufficiently high power so as to cause changes in opticalproperties of the record carrier, which changes become manifest by areduced reflection of the radiation pulses, characterized in that themethod comprises a preparatory step of providing marks on the recordcarrier by locally heating the record carrier with radiation pulseshaving a first power, followed by a first measuring step of determininga second power (P_(min)) of the radiation pulses, at which power theoptical properties of the record carrier at the location of the marksprovided in the preparatory step do not substantially change when therecord carrier is irradiated at a power which is lower than said secondpower, and the optical properties of the record carrier at the locationof the provided marks change to such an extent that the normalizedreflected power increases, when the record carrier is irradiated at apower which is higher than said second power, and a second measuringstep of determining a third power (P_(max)) of the radiation pulses, atwhich power the optical properties of the record carrier change when therecord carrier is irradiated at said third power at the location of themarks provided in the preparatory step, such that the normalizedreflected power becomes maximal, followed by a comparison step ofdetermining the optimal erase power (P_(EO)) from the equation$P_{EO} = {\beta \cdot \frac{\left( {P_{\min} + P_{\max}} \right)}{\alpha}}$

in which α is a constant known in advance and β is a variable which isdependent on properties of the record carrier.
 2. A method ofdetermining the optical write power for providing marks in an opticalrecord carrier, which marks are provided by locally heating the recordcarrier with radiation pulses having a sufficiently high power so as tocause changes in optical properties of the record carrier, which changesbecome manifest by a reduced reflection of the radiation pulses,characterized in that the method comprises a preparatory step ofproviding marks on the record carrier by locally heating the recordcarrier with radiation pulses having a first power, followed by a firstmeasuring step of determining a second power (P_(min)) of the radiationpulses, at which power the optical properties of the record carrier atthe location of the marks provided in the preparatory step do notsubstantially change when the record carrier is irradiated at a powerwhich is lower than said second power, and the optical properties of therecord carrier at the location of the provided marks change to such anextent that the normalized reflected power increases, when the recordcarrier is irradiated at a power which is higher than said second power,and a second measuring step of determining a third power (P_(max)) ofthe radiation pulses, at which power the optical properties of therecord carrier change when the record carrier is irradiated at saidthird power at the location of the marks provided in the preparatorystep, such that the normalized reflected power becomes maximal, followedby a comparison step of determining the optimal write power (P_(WO))from the equation$P_{WO} = {\delta \cdot \beta \cdot \frac{\left( {P_{\min} + P_{\max}} \right)}{\alpha}}$

in which α is a constant known in advance and β and δ are variableswhich are dependent on properties of the record carrier.
 3. A method asclaimed in claim 1 or 2, characterized in that the first measuring stepcomprises at least two sub-steps, in which sub-steps the record carrieris irradiated at the location of the provided marks with radiationpulses having a test power of a selected value, which test powerincreases in the consecutive sub-steps as long as the optical propertiesof the record carrier at the location of the irradiated marks do notsubstantially change, and which sub-steps are terminated as soon as theoptical properties of the record carrier at the location of theirradiated marks change to such an extent that the normalized reflectedpower increases, followed by a first final step in which the value ofthe test power in the last sub-step is allocated to the second power(P_(min)).
 4. A method as claimed in claim 1 or 2, characterized in thatthe second measuring step comprises at least two sub-steps, in whichsub-steps the record carrier is irradiated at the location of theprovided marks with radiation pulses having a test power of a selectedvalue, which test power increases in the consecutive sub-steps, andwhich sub-steps are terminated as soon as the optical properties of therecord carrier at the location of the irradiated marks change to such anextent that the normalized reflected power decreases, followed by asecond final step in which the value of the test power in the lastsub-step is allocated to the third power (P_(max)).
 5. A method asclaimed in claim 1 or 2, characterized in that the marks, which areprovided in the preparatory step, are of a maximum length which maximumlength is the maximum length allowed by the applied coding method.
 6. Amethod as claimed in claim 5, characterized in that the marks, which areprovided in the preparatory step, are coded with an I11 carrier inaccordance with the EFM+ (Eight-to-Fourteen Modulation Plus) codingmethod.
 7. A method as claimed in claim 1 or 2, characterized in thatthe marks, which are provided in the preparatory step, are provided inselected distinguishable areas.
 8. A method as claimed in claim 7,characterized in that the selected distinguishable areas are evenlyspread across the surface of the record carrier.
 9. A method as claimedin claim 1 or 2, characterized in that the factor a in the comparisonstep has a value of
 2. 10. A method as claimed in claim 1 or 2,characterized in that the factor α in the comparison step has a value of2 and the factor β in the comparison step has a value of between 0.7 and1.3.
 11. A method as claimed in claim 1 or 2, characterized in that thefactor β in the comparison step is read from an area on the recordcarrier, which area comprises information about properties of the recordcarrier.
 12. A method as claimed in claim 2, characterized in that thefactor δ in the comparison step is read from an area on the recordcarrier, which area comprises information about properties of the recordcarrier.
 13. An optical record carrier for use in one of the methods asclaimed 1 or 12, inscribable by a radiation beam, containing an areacomprising information about properties of the optical record carrier,characterized in that the area comprising information about propertiesof the record carrier comprises a value for the factor β used in thecomparison stage of the method.
 14. An optical record carrier for use inone of the methods as claimed in claim 1 to 12, inscribable by aradiation beam, containing an area comprising information aboutproperties of the optical record carrier, characterized in that the areacomprising information about properties of the record carrier comprisesa value for the factor δ used in the comparison stage of the method. 15.A recording apparatus comprising a calibration device for determiningthe optimal erase power required for erasing marks provided in anoptical record carrier of the type in which marks are provided bylocally heating the record carrier with radiation pulses having asufficiently high power so as to cause changes in optical properties ofthe record carrier, which changes become manifest by a reducedreflection of the radiation pulses, characterized in that thecalibration device is adapted to provide marks on the record carrier bylocally heating the record carrier with radiation pulses having a firstpower, and to determine a second power (P_(min)) of the radiationpulses, at which power the optical properties of the record carrier atthe location of the provided marks do not substantially change when therecord carrier is irradiated at a power which is lower than said secondpower, and the optical properties of the record carrier at the locationof the provided marks change to such an extent that the normalizedreflected power increases, when the record carrier is irradiated at apower which is higher than said second power, and to determine a thirdpower (P_(max)) of the radiation pulses, at which power the opticalproperties of the record carrier change when the record carrier isirradiated at said third power at the location of the provided marks,such that the normalized reflected power becomes maximal, and todetermine the optimal erase power (P_(EO)) from the equation$P_{EO} = {\beta \cdot \frac{\left( {P_{\min} + P_{\max}} \right)}{\alpha}}$

in which α is a constant known in advance and β is a variable which isdependent on properties of the record carrier.
 16. A recording apparatuscomprising a calibration device for determining the optimal write powerrequired for providing marks in an optical record carrier, which marksare provided by locally heating the record carrier with radiation pulseshaving a sufficiently high power so as to cause changes in opticalproperties of the record carrier, which changes become manifest by areduced reflection of the radiation pulses, characterized in that thecalibration device is adapted to provide marks on the record carrier bylocally heating the record carrier with radiation pulses having a firstpower, and to determine a second power (P_(min)) of the radiationpulses, at which power the optical properties of the record carrier atthe location of the provided marks do not substantially change when therecord carrier is irradiated at a power which is lower than said secondpower, and the optical properties of the record carrier at the locationof the provided marks change to such an extent that the normalizedreflected power increases, when the record carrier is irradiated at apower which is higher than said second power, and to determine a thirdpower (P_(max)) of the radiation pulses, at which power the opticalproperties of the record carrier change when the record carrier isirradiated at said third power at the location of the provided marks,such that the normalized reflected power becomes maximal, and todetermine the optimal write power (P_(WO)) from the equation$P_{WO} = {\delta \cdot \beta \cdot \frac{\left( {P_{\min} + P_{\max}} \right)}{\alpha}}$

in which α is a constant known in advance and β and δ are variableswhich are dependent on properties of the record carrier.
 17. Acalibration device for use in a recording apparatus as claimed in claim15 or 16.